1. Field of the Invention
Exemplary embodiments of the present invention relate to an apparatus and a method for loop-back in wireless communication systems, and more particularly, to an apparatus and a method for loop-back data to be transmitted to a medium access layer between a medium access layer and a physical layer in wireless communication systems.
2. Description of Related Art
Generally, a loop-back scheme for returning original data to a sender without transmitting the data to a receipt by feedbacking the data to a transmitting apparatus without transmitting the data from the transmitting apparatus transmitting the data to a receiving apparatus in a communication system has been prevalently used. The loop-back scheme has been used as various purposes. However, the most important purpose of the loop-back scheme is to verify integrity of a communication path that is being currently used.
For example, in a wired network such as an asynchronous transfer mode (hereinafter, referred to as “ATM”) or Ethernet, the loop-back uses a line loop-back method of connecting a cable line that is a channel transmitting data from a physical layer (PHY) to a receiving unit of the sender transmitting data rather than an opponent receipt receiving the data. As another loop-back scheme, there is a scheme of loop-backing the data to be transmitted between the medium access layer (hereinafter, referred to as “MAC”) of the sender and the physical layer without performing a handover to the physical layer and allowing the receiving unit of the MAC to receive the data, or the like.
However, unlike the wired network, it is difficult to adopt loop-back technologies of the wired network as they are due to characteristics of the wireless communication systems to be accessed to a shared medium called the wireless channel. In particular, unlike a carrier sensing multiple access/collision detection (hereinafter, referred to as “CSMA/CD” of wired Ethernet) scheme, the wireless access network of Institute of Electrical and Electronics Engineers 802.11 (IEEE 802.11) based wireless access network uses a carrier sensing multiple access/collision avoidance (CSMA/CA) method and thus, it is difficult to adopt a loop-back technology as it is in the existing wired Ethernet.
For example, in the wired Ethernet, detecting a carrier and then, immediately transmitting data when the wired channel is empty and confirming whether the data originally reach the receipt are considered that the data are originally transmitted to a receipt when collision does not occur through collision detection (CD). On the other hand, in the 802.11 based wireless access technology, a sender secures the shared wireless channel and then, transmits data to be transmitted through a process of first transmitting a control frame to the receipt after sensing the carrier and allowing a receipt to transmit a response control frame thereto to a sender.
In addition, in the 802.11 based wireless access technology, unlike the wired Ethernet depending on the collision detection, confirming whether the data originally reach the receipt transmits the control frame having a meaning that the receipt receives the data well to the sender and the sender determines that the data reach the receipt as they are only when the sender receives the control frame as it is.
Therefore, in the 802.11 based wireless access technology, when implementing the loop-back function, like the wired Ethernet, when all the frames transmitted by the sender are loop-backed as they are, two problems may occur as follows. First, the sender transmits the control frames to be transmitted before transmitting data. This waits for the response frame of the receipt to the control frame transmitted by the sender so as to allow the sender to transmit the data when the control frames are simply loopbacked to the sender. However, the sender cannot permanently receive the response frame of the receipt since the control frame transmitted by the sender are loopbacked and thus, are not transmitted to the receipt, thereby failing to secure the wireless channel.
Second, when simply loop-backing the data transmitted by the sender that the receipt is expected to transmit the receive acknowledgement ACK to the sender, the data transmitted by the sender are loop-backed and thus, the sender does not permanently receive the ACK message to the data transmitted by the sender. Therefore, the normal data transmission is considered as being failed.
Accordingly, in the 802.11 based wireless communication systems, since the share wireless channel access method is different from the existing wired network, it is impossible to apply the existing loop-back technology as it is. Therefore, a need exists for a new loop-back method considering unique characteristics of the wireless communication systems.